8 Answers
8

Most mobile phone service providers (in the USA, at least) automatically set up email addresses that will pass through as SMS messages to cell phones.

For example, if I am on AT&T and my phone number is (123) 456-7890, then anyone can send an email to 1234567890@txt.att.net and it will be sent to my phone. If I reply to the SMS message from my phone, it will be emailed back to the original sender.

Another problem I found with this approach was that AT&T generated a new "from" number for each email received. That made it impossible to group messages from the same sender into conversations. I wound up getting a Google Voice account.
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cjmMar 15 '13 at 21:55

pinger textfree web allows you to do this, at least, to start a new Gmail account (viz. accept text messages on a local number). I haven't tried to automate anything. They use bot-tests like everybody else.

But if you want API-level access there is a company that makes a famously accessible (albeit paid if you want more than a few requests per hour) API service called Twilio.

I've been using Sooeet Text to send and receive free SMS (text only) and MMS (text and picture) messages online. You don't have to register to use it, but if you do register it remembers your text dialogue and the phone numbers that you texted.

Google just added SMS capability to Gmail and it’s free. Here is how to do it:

Log in to Gmail

You have to enable SMS Texting first by going into Settings → Labs tab, then click Enable on the SMS (text messaging) in Chat option.

After you enable SMS messaging in chat, make sure your friends list is showing on the left-hand side menu. There should be a little search box all the way to the left where you can type someone's name, and a green light next to your profile picture. If it's not showing, you can click the little "Txt Message Bubble Icon" on the very bottom of the left hand menu column.

In the box on the left hand menu, it should say "Search, Chat, or SMS". Type in the number or name of the contact you want to text, and then a menu will pop up and click Send SMS and there you go!

You do not need to know which cell provider they have or anything else, and I think that if you get a response it should show up right in your chat window.